• Journal of the Korean Society for Precision Engineering
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• v.26 no.7
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• pp.51-57
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• 2009

In this paper, we studied on an attenuation effect of automobile exhaust noise according to the direction of canceling speaker in duct-acoustic ANC system. Automobile exhaust noise was recorded at 800rpm, 3500rpm and 5000rpm of a diesel engine. Directions of canceling speaker can be set to $30^{\circ}$, $90^{\circ}$ and $150^{\circ}$ against the primary noise flow by acrylic ducts to be made for the experimentation. DSP board used to control the ANC system. The algorithm of this ANC system applied the Filtered-x-LMS algorithm that is modified to compensate for a property of DSP input signal and the secondary-path effect. As an experiment result, the direction of canceling speaker was proved to influence the reduction effect of noise. The $150^{\circ}$ duct in the attenuation effect of noise showed a better result than the $90^{\circ}$ or $30^{\circ}$ duct.

• Journal of Magnetics
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• v.10 no.4
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• pp.163-170
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• 2005

The RF integrated noise filters are fabricated by photolithography. The stack for the electromagnetic noise filters consists of the nano-granular ($Co_{41}Fe_{38}AI_{13}O_8$) soft magnetic film / $SiO_2$ / Cu transmission line / seed layer (Cu/Ti) / $SiO_2$-substrate. A good signal-attenuation feature along with a low signal-reflection feature is observed in the present filters. Especially in the noise filter incorporated with a $Co_{41}Fe_{38}AI_{13}O_8$ magnetic film with lateral dimensions of $2000{\mu}m$ wide, 15 mm long and $1{\mu}m$ thick, the maximum magnitude of signal attenuation reaches -55 dB, and the magnitude of signal reflection is below -10 dB in the overall frequency range. And this level of signal attenuation is much larger than that of a noise filter incorporated with a Fe magnetic film.

• Journal of KSNVE
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• v.8 no.4
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• pp.733-740
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• 1998

본 논문은 덕트 내에 설치된 음향 스크린의 특성을 연구하였다. 다양한 형상의 음향 스크린의 투과 손실 측정을 통하여, 음향 스크린에 의해 생긴 두 개의 비대칭 경로가 특정 주파수에서 큰 협대역 소음 저감을 발생시킴을 알 수 있었다. 그리고, 실험과 수치적 모의 실험을 바탕으로 이러한 현상을 정확하게 설명할 수 있는 해석적 모델을 개발하였다.

• Journal of the Korean housing association
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• v.9 no.2
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• pp.67-78
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• 1998

Construction equipment noise has caused much annoyance for a number of dwellers in nearby construction field and it has become a very serious issue in our living environment. Therefore, in our country, a practical solution and a better method of reducing construction equipment noise are highly required in construction field. Practical solutions for the construction equipment noise, however, are very difficult to obtain, because of the lack of basic data and insufficient research works. Especially, in order to establish a successful sound isolation plan for piling work noise, which has high sound pressure level, the characteristics of the impact noise should be closely monitored and analyzed. This study attempts to survey the characteristics of attenuation and propagation of construction equipment noise in piling work by SIP(soilcement injected precast pile) method. In addition, this study intends to get the basic data to establish a standard about construction noise.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.18 no.1
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• pp.101-108
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• 2019

In this study, the hole-cavity resonance technology and the micro pore stainless chip sintering technology were fused to develop silencers with excellent noise attenuation performance even at fluid pressures exceeding 30 bar for the first time at home and abroad. As a result of this study, the noise attenuation performance was greatly improved as reflection, loss, and resonance were made to occur thousands of times simultaneously when fluids pass through the sintered micro pore stainless steel chip sound absorber. The noise of the gas emitted from the bomb without the silencer was shown to be 125dB. And noise test conducted after installation of the silencer showed the noise of 67dB. Given the study results, the amount of noise was greatly reduced in the sintered silencer.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.6
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• pp.413-419
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• 2002

Noise barriers are widely used to reduce the sound level propagating from highways, railways or factories to residential areas. The reduced noise level at a receiver point is then determined by the diffracted waves around the edge of the barrier as well as by the transmitted waves through the barrier. 1'or proper usage, many studies either theoretical or experimental have been made with the objective of precisely Predicting the acoustic field and improving the noise attenuating properties of barriers. In this study. a simple scattering model. a line acoustic source scattered by an infinite cylinder, is introduced to simply Investigate the sound attenuation efficiency of a sound-resonating barrier. From this model study, it is observed that the sound-resonating harrier can be used as a good sound-shielding element especially for the pure-tone noise generated from the transformer. Large sound-attenuation is achieved by applying the sound-resonating barrier to the large transformers in a substation.

• International Journal of Fuzzy Logic and Intelligent Systems
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• v.15 no.1
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• pp.20-26
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• 2015

It is very difficult to design an underwater communication system because of multipath, Doppler effects, noise, and attenuation. These factors lead to errors in the communication performance and maximum propagation distance. In this study, we calculate the distance that can be realized using the direct-sequence code division multiple access (DS-CDMA) technique with direct-sequence spread spectrum (DSSS) in an underwater communication system considering only the attenuation and noise. We also compare the estimated and calculated propagation distances obtained for several different scenarios.

• Proceedings of the KIEE Conference
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• 2006.07b
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• pp.1002-1003
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• 2006

Power line communication: PLC which easy to install at anywhere near outlet for electric machine. PLC uses transmission line for voltage of which is 60 Hz. One of the important thing is the processes of adding signal to power line and extracting the signal from power line, another is to choose the strong modulation method which sends signals to long distance without loosing in PLC channel. but PLC channel have very high and variable noise and attenuation and then it is very hard to transmit optimally between the transmitter and the receiver. AWGN, impulse noise and attenuation are created. To overcome the noise and attenuation. Multi-carrier Modulation methods like as OFDM and DMT which divide the channel into many sub-channel are powerful communication methods for PLC. In this paper, PLC channels are simulated for getting BER by Matlab simulink

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.11
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• pp.1013-1019
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• 2011

Sound attenuation of periodically arranged cylindrical rods is studied numerically and experimentally. Cross section of the cylinder is circular and arrays are in a square lattice. Cylinders are made of steel, and consist of five groups with different diameters from 27.2 mm to 48 mm. Each group has 5 rows, while number of cylinders in a row varies from 17 to 31. The area filling fraction is about 60~61 %, which leads to the stop bandgap(2.9 kHz ~ 8.4 kHz). Sound attenuation is computed using two-dimensional BEM, and measurement is done by using a speaker and microphones in a semi-anechoic room. Comparison of the results by BEM and experiment shows that attenuation spectra are qualitatively in agreement, although experiment gives higher attenuations than BEM. After results by BEM are scaled up in accordance with cylinder diameter, it is observed that attenuation curves are in good agreement, which confirms that analysis by BEM is done correctly. It is also found that the measured bandgaps are shifted toward lower frequency by 0.5 kHz ~ 1.2 kHz, when compared to the predictions obtained from infinitely repeated two-dimensional cylinder arrays.

• Journal of Electrical Engineering and Technology
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• v.13 no.1
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• pp.430-437
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• 2018

Ultrasonic attenuation is an important parameter in Quantitative Ultrasound and many algorithms have been proposed to improve estimation accuracy and repeatability for multiple independent estimates. In this work, we propose an improved algorithm for estimating ultrasonic attenuation utilizing the optimal frequency compounding technique based on stochastic noise model. We formulate mathematical compounding equations in the AWGN channel model and solve optimization problems to maximize the signal-to-noise ratio for multiple frequency components. Individual estimates are calculated by the reference phantom method which provides very stable results in uniformly attenuating regions. We also propose the guideline to select frequency ranges of reflected RF signals. Simulation results using numerical phantoms show that the proposed optimal frequency compounding method provides improved accuracy while minimizing estimation bias. The estimation variance is reduced by only 16% for the un-compounding case, whereas it is reduced by 68% for the uniformly compounding case. The frequency range corresponding to the half-power for reflected signals also provides robust and efficient estimation performance.